The present invention relates to a structure for mounting a thermal fuse on a circuit board, for example, a structure for mounting an axial type thermal fuse on a circuit board placed in a small space like a circuit board contained in a battery casing of a notebook computer or the like. More specifically, the invention relates to a structure for mounting a thermal fuse on a circuit board in which the thermal fuse is attached to sensitively detect the temperature of any component as its temperature increases and which enables reduction of the total thickness of the circuit board including mounted components.
A battery casing of a notebook computer contains, as shown in FIG. 2 for example, a rechargeable battery such as lithium ion battery or the like encased in a battery housing 22 in a resin case 21. In a narrow space between battery housing 22 and an end of resin case 21, an electric circuit board 23 is housed. Electric circuit board 23 has components formed thereon such as a protection circuit for preventing overcharge of the rechargeable battery as well as explosive breakdown due to short-circuit.
Onto circuit board 23, a thermal fuse is integrated in the vicinity of any electronic component such as FET which readily generates heat when overcurrent flows due to occurrence of abnormality on a circuit. Circuit board 23 is thus provided with means for preventing such an accident by breaking the circuit when the temperature abnormally increases.
In a conventional mount structure for a circuit board having such a thermal fuse, as shown in FIGS. 3A and 3B for example, a silicone resin 33 is applied onto a board 31 to reach an FET 32 thereby facilitate heat conduction from FET 32 which readily generates heat. An axial type thermal fuse 34 is mounted on silicone resin 33 to be embedded therein and connected in series to the circuit. Therefore, when viewed from the side of thermal fuse 34, silicone resin 33 is higher than thermal fuse 34 while thermal fuse 34 is surrounded by silicone resin 33 with the upper surface of thermal fuse 34 being exposed.
As discussed above, in the conventional mount structure having the thermal fuse integrated onto the circuit board, the silicone resin for temperature transmission is applied onto the board, the thermal fuse is mounted on the silicone resin and accordingly, the thickness (H in FIG. 3B) from the board increases.
A resultant problem is, for such a use as the one which requires the thickness H from the board to be 4 mm or less like a thin circuit board or the like used for the battery casing of the notebook computer described above, a considerable difficulty in dimensioning the circuit board in such a range because the diameter D of the thermal fuse is approximately 2 mm, leading to deterioration of working efficiency.
The entire thickness could be reduced by decreasing the thickness of board 31. However, currently the board is approximately 0.8 mm in thickness, and further thinning of the board would cause warp thereof. Consequently, the mounting work becomes troublesome in manufacture and the cost of the board increases.
The present invention is made to solve these problems. One object of the invention is to provide a mount structure for a thermal fuse on a circuit board, which enables reduction of the thickness to the surface of mounted components without thinning the board, allows a thermal fuse to be mounted on a circuit board housed in a considerably small space such as the one in a notebook computer, and further enables circuit to be broken surely when any abnormality occurs by sensitively detecting the temperature of any component which is likely to increase in temperature.
According to the present invention, a mount structure for thermal fuse on circuit board includes a circuit board, a through opening, an electronic component and a thermal fuse. The circuit board has one surface on which a predetermined circuit is formed. The through opening is provided in the circuit board. The electronic component is attached to the one surface of the circuit board to extend across the through opening. The thermal fuse is provided on the other surface of the circuit board to enter the through opening, responding to the temperature of the electronic component via a heat-conducting insulating member filling the through opening for breaking the predetermined circuit. In particular, the electronic component here refers to an electronic component such as power FET for example having its temperature remarkably increased when any abnormality such as overcurrent occurs.
In this structure, the electronic component is attached to one surface of the circuit board to extend across the through opening provided in the circuit board, and for this particular electronic component, the thermal fuse is provided on the other surface of the circuit board to enter the through opening. In this way, it is possible to reduce the thickness of the entire assembly. The temperature of the electronic component is conducted to the thermal fuse via the heat-conducting insulating member filling the through opening. Accordingly, any temperature increase of the particular electronic component can be monitored sensitively, which ensures breaking of the circuit in the event of temperature increase.
Specifically, the heat-conducting insulating member described above is preferably silicone resin.
Preferably, a through hole is provided in the circuit board and the thermal fuse is electrically connected to the predetermined circuit via the through hole.
In this case, the thermal fuse attached to the other surface of the circuit board can readily be connected to the circuit formed on one surface of the circuit board.
Further, the thermal fuse preferably includes therein a rod-shaped fuse.
In this case, depending on use or heat-conducting state between the fuse and the electronic component, the diameter of the rod-shaped fuse can be changed to easily control the temperature at which the circuit is to be broken.